Sealing between two flat-faced casings is very often provided by the combined use of a flat semi-plastic synthetic material seal (stamped gasket or slow setting adhesive) and clamping, or fixing means generally formed of a number of screws (or stud bolts and nuts). In the general case, which interests us here, the elastomer material seal, of an O-seal type for example, is housed in a groove formed in the flat face of one of the casings, in contact with the flat face of the other casing. The constant cross-sections of the groove and of the seal are of course determined so that, after clamping of the fixing means, a portion of the seal remains projecting from the face of the casing in which the groove is formed and remains in contact with the face of the opposite casing.
This system generally gives satisfaction when the casings are made from metal, particularly in the case of casings for cooling water pumps for motor vehicles. However, when the operating temperatures are increased, this solution becomes precarious because of the relative expansion and the lesser degree of clamping in the portions situated between the fixing screws. It then frequently happens that leaks appear precisely in these portions. This defect is further accentuated when one of the casings is made from a plastic, thermoplastic or heat hardenable material, for hot flowing of these materials is greater than for metals.
Furthermore, under stress, an elastomer tends to free itself from this stress by flowing, i.e. by a reduction of thickness, this thickness tending towards a limit value representing what is called remanence. To take this reduction into account, which is a certain percentage of the initial thickness, it is necessary, all other things being equal, to give to the seal the greatest possible thickness so as to keep maximum clamping. This requirement is felt all the more so since loosening or gaping may occur between the fixing points.
But the thickness of the seal is limited by the very arrangement of the means fixing the casings together. This arrangement, which aims at reducing as much as possible the risks of gaping, leads, in the vicinity of these fixing means, to leaving very often, for the groove housing the seal, only a fairly small space, so fairly small groove width, and consequently a limited seal thickness.
It can be seen, for the above mentioned reasons, that it is then the quality of sealing itself which is in question.
To overcome these drawbacks partially, the documents SU-A-697 774 and U.S. Pat. No. 3,913,927 propose seals with evolutive cross-section. However, with such an approach, control of the compression of the seal is imperfect to the extent that it depends mainly on the deformation of the parts between which the seal is located.